The present invention relates to a semiconductor light emitting device, such as a semiconductor laser and a light emitting diode, which uses a compound of a Group III element and nitrogen (a Group III nitride type, gallium nitride type compound semiconductor) and is capable of emitting light in the blue area that is required for an optical disk memory having a high storage density and for a high-precision laser beam printer. More specifically, the present invention concerns a semiconductor light emitting device in which a conductive substrate is used as a substrate on which a semiconductor layer having a superior light emitting property is laminated, and electrodes can be taken out from both of the upper and lower surfaces of a chip and is allowed to have a cleavage, and also concerns a semiconductor laser on which such a semiconductor light emitting device and its chip is mounted with a superior heat radiating property.
With respect to blue-type semiconductor lasers, for example, Japanese Journal of Applied Physics (Jpn. J. Apply. Phys.) Vol. 35 (1996), pp 74-76, has reported a construction in which a CW oscillation is available in the blue area. As illustrated in FIG. 19, hexagonal system Group III nitride compound semiconductors are successively stacked on a sapphire substrate 71 by metal organic chemical vapor deposition (hereinafter, referred to as MOCVD); that is, the following layers are stacked: a GaN buffering layer 72, an n-type GaN layer 73, an n-type stress alleviating layer 74 made from In0.1Ga0.9N, an n-type clad layer 75 made from Al0.12Ga0.88N, an n-type light guide layer 76 made from GaN, an active layer 77 made of a multiple quantum well structure of an InGaN type compound semiconductor, a p-type light guide layer 78 made from p-type GaN, a p-type first clad layer 79 made from p-type Al0.2Ga0.8N, a p-type second clad layer 80 made from Al0.12Ga0.88N and a contact layer 81 made from a p-type GaN. One portion of this semiconductor layers thus stacked is then etched by dry etching, etc. so that, as illustrated in FIG. 19, n-type GaN layer 73 is exposed to outside, and an n-side electrode 83 is formed on the surface thereof, and a p-type electrode 82 is formed on the aforementioned contact layer 81 respectively.
Moreover, Japanese Patent Notifying Publication No. 8217/1996 (Tokukouhei 8-8217) discloses a method in which a GaaAl1xe2x88x92aN (0 less than axe2x89xa61) serving as a buffering layer is formed, and a gallium nitride type compound semiconductor is stacked thereon.
However, in any of these methods, since the semiconductor layers are stacked on the sapphire substrate, the n-side electrode has to be formed on the n-type layer that has been exposed by etching one portion of the stacked semiconductor layers. Moreover, since the sapphire substrate is very hard, it is very difficult to provide a cleavage; therefore, the laminated layers of the Group III nitride compound semiconductor are again etched by dry etching to form an end face constituting a light resonator.
In the conventional blue-type semiconductor light emitting device, since a sapphire substrate is used as the substrate, it is not possible to form a vertical type element (referred to as a construction in which electrodes are formed on both of the upper and lower surfaces, and hereinafter, the same is true ) having electrodes formed on both of the upper and lower faces of the laminated layer. For this reason, complex manufacturing processes are required, a complex chip bonding process is also required, and it is not possible to provide a cleavage, resulting in a failure in forming a flat end face from the atomic point of view.
Moreover, Patent Publication No. 2677221 discloses a method for laminating a Group III nitride compound semiconductor on a gallium arsenide substrate. In this method, a buffer layer of GaN, etc. is formed at a low temperature of approximately 350 to 530xc2x0 C. by using a hydride vapor-phase epitaxial method, and a semiconductor laminated portion is then allowed to grow. However, in this method gallium nitride type compound semiconductor such as GaN is directly formed on a GaAs substrate, with the result that in comparison with a GaAs lattice constant of 5.6537 xc3x85, cubic GaN has a lattice constant of approximately 4.5 xc3x85, which is a greatly different value. For this reason, a highly unconformity hetero-epitaxial growth takes place, frequently resulting in a defective stacked layer; therefore, it is difficult to reduce the transition density to an extent necessary to emit laser light, and from the viewpoint of crystalline property, this method is more difficult than the method for laminating a gallium nitride type compound semiconductor layer on a sapphire substrate.
Moreover, another structure has been known in which a gallium nitride type compound semiconductor is stacked on a silicon carbide substrate with an AlN or GaAlN type semiconductor layer being provided as a buffer layer. However, in this structure also, in the same manner as the case where the lamination is made on the sapphire substrate, a hexagonal system gallium nitride type compound semiconductor is laminated at a high temperature, and a hexagonal-system-use silicon carbide substrate is adopted. Therefore, a substrate that is by far more expensive substrate than a sapphire substrate has to be used, and the substrate costs virtually 20 times as expensive as the sapphire substrate, resulting in a failure in putting this method into practical use.
As described above, the conventional blue-color semiconductor laser has the structure in which a Group III nitride compound semiconductor layer is laminated on a sapphire substrate, and sapphire has a thermal conductivity of 0.46 W/(cmxc2x7K), which is extremely smaller than that of Si (thermal conductivity 1.7 W/(cmxc2x7K)), etc. In the blue color semiconductor laser, since its wavelength is particularly short and since the Group III nitride compound semiconductor layer is inferior in the crystalline property, and tends to generate heat, its heat radiating efficiency gives greatly influences on the property and reliability of the semiconductor laser, as described earlier. For this reason, as shown in Japanese Unexamined Patent Application No. 235729/1995 (Tokukaihei 7-235729) as well as in FIG. 20, an upper p-side electrode 82 close to the active layer is die-bonded through a bonding agent 92 such as solder so as to directly contact a sub-mount 90, with the chip facing down. In this case, as described earlier, the n-side electrode 83 is formed in a concave section, and there is a step difference between the p-side electrode 82 and the n-side electrode 83; therefore, the die-bonding has to be carried out with solder agent 91 corresponding to the thickness being interpolated in between, or as illustrated in FIG. 21, a step difference is formed on the surface of the sub-mount 90, and the bonding is carried out with the step difference of the LD chip 70 being coincident with this step difference.
As described above, in the blue color LD chip using the conventional Group III nitride compound semiconductor, the Group III nitride compound semiconductor is laminated on the sapphire substrate; therefore, in order to carry out a mounting process so as to increase the heat-radiating efficiency, the die-bonding has to be carried out with thick solder agent 91 being interpolated on the side of the concave n-side electrode 83, or the mounting has to be carried out with the step difference of the LD chip 70 being coincident with the step difference formed on the surface of the sub-mount 90. However, in the case of the thick solder agent 91, it is highly possible that, when the solder agent 91 is fused, solder flows onto the laminated semiconductor layer (on the side wall exposed by etching), causing short-circuiting between the laminated n-type layer and the p-type layer or causing much current leakage. Moreover, in the case when the step difference is formed on the sub-mount, the step difference has a width of approximately several xcexcm, and since there are some deviations, it is difficult to supply a large number of sub-mounts having a step difference coincident with the step difference of the LD chip, and to mass-produce a semiconductor laser with high yield. Furthermore, since a LD chip is smaller than 1 square mm, the gap between the two electrodes on the p-side and n-side that are placed on the same face side is also very small, frequently resulting in a problem of short-circuiting between the electrodes.
One objective of the present invention is to provide a semiconductor light emitting device at low costs, which is of a vertical type that allows electrodes to be taken out from both of the upper and lower surfaces of a chip, has a superior crystalline property in the semiconductor layer with a high light emitting efficiency, and uses a Group III nitride compound semiconductor.
Another objective of the present invention is to provide a semiconductor laser which can form a light emitting face by utilizing a cleavage so that an end face that is superior in flatness is obtained.
Still another objective of the present invention is to provide a semiconductor laser which has a vertical type chip that allows electrodes to be taken out from both of the upper and lower surfaces thereof, while using a Group III nitride compound semiconductor, and which is bonded to a sub-mount with high reliability, and efficiently radiates heat to the sub-mount.
Still another objective of the present invention is to provide a semiconductor laser having a structure in which the sub-mount can radiate heat more efficiently, and both of the electrodes of the chip can be easily electrically connected to a device side such as a stem through the sub-mount.
Still another objective of the present invention is to provide a semiconductor laser having a structure in which: an insulating sub-mount having a superior thermal conductivity is used and the respective electrodes of the LD chip are easily connected to a heat sink such as a stem without being embedded in a metal rod.
Still another objective of the present invention is to provide a semiconductor light emitting device such as an LD and its manufacturing method, which reduces the threshold current of a semiconductor light emitting device using a Group III nitride compound semiconductor so that the quantum differential efficiency is improved, a higher output is obtained by using a low operational voltage, and a light emission having a wavelength longer than that of blue light is available.
The other objective of the present invention is to provide a semiconductor laser which can reduce the threshold current of the laser and improve the output characteristic so that an appropriate current constriction layer is formed in a GaN type compound semiconductor layer.
In this case, the compound semiconductor of a Group III element and nitrogen refers to a semiconductor made from a compound between Ga that is a Group III element and N that is a Group V element or a compound in which one portion or all the portion of Ga that is a Group III element is substituted by another Group III element such as Al and In, and/or a compound in which one portion of N that is a Group V element is substituted by another Group V element such as P and As. This is also referred to as a Group III nitride compound semiconductor or a gallium nitride type compound semiconductor.
For example, the buffer layer is formed as a layer made from GaNxAs1xe2x88x92x (0 less than x less than 1), or it is allowed to have a composition of gallium arsenide or a composition close to that of gallium arsenide on the substrate side, and also allowed to have a composition of the semiconductor layer that forms the lowermost layer of the semiconductor lamination section or a composition close to that of the semiconductor layer on the semiconductor lamination section side. Here, in the case when the semiconductor lamination section is made from a Group III element nitride compound, not limited by the composition of the lowermost layer of the semiconductor lamination section, for example, even when it is allowed to have a composition of GaN or a composition close to GaN, the problem of the lattice constant unconformity will not particularly arise. Here, for example, the composition closer to GaN refers to a compound in which a slight portion of Ga and/or N is substituted by another element.
In the case when the above-mentioned substrate is made from germanium, the buffer layer may be formed by AlzGa1xe2x88x92zN (0xe2x89xa6zxe2x89xa61).
In the case when the semiconductor lamination section has a structure in which it is sandwiched between an active layer and the n-type layer and p-type layer having greater band gap energy than the active layer, the light emitting efficiency is enhanced, and a high luminance light emitting diode or semiconductor laser is obtained.
A semiconductor laser is provided with a substrate made from a gallium arsenic compound, a buffer layer containing at least arsenic, nitrogen and gallium, formed on the substrate, and a semiconductor lamination section which is formed on the buffer layer, and is made of a compound semiconductor of a Group III element and nitrogen, with the active layer being sandwiched between the n-type layer and the p-type layer having a band-gap energy greater than the active layer, and the semiconductor lamination section is formed in such a manner that the refractive index of the active layer is set to be greater than the refractive index of each of the n-type layer and p-type layer.
In the case when the semiconductor lamination section is laminated so as to have a cubic crystal system and the light emitting face of the active layer is formed by a cleavage face, it is possible to form a resonator having an end face that is superior in the flatness, and consequently to obtain a semiconductor laser having a great output.
Specifically, this structure may be provided with a gallium arsenide substrate, a buffer layer that is placed on the substrate, and made from GaNxAs1xe2x88x92x (0xe2x89xa6xxe2x89xa61) with x varying successively, and a semiconductor lamination section having a first conductivity type clad layer formed on the buffer layer, a first conductivity type light guide layer, an active layer, a second conductivity type light guide layer and a second conductivity type clad layer. Here, the expression, x varying successively, refers to both of the cases in which it varies step by step and it varies successively.
More specifically, the structure may be further provided with a first electrode formed on the rear face of the gallium arsenide substrate, a contact layer formed on the semiconductor lamination section and a second electrode having a striped shape, formed on the contact layer.
A semiconductor light emitting device of the present invention is provided with a silicon substrate, a silicon carbide layer formed on the silicon substrate, and a semiconductor lamination section which is formed on the silicon carbide layer, made from a compound semiconductor of a Group III element and nitrogen, has at least an n-type layer and a p-type layer, and is laminated so as to form a light emitting layer.
In this structure, the semiconductor lamination section made of the compound semiconductor of the Group III element and nitrogen is formed on the silicon substrate through the silicon carbide layer; therefore, with respect to the lattice constant of silicon and silicon carbide, silicon has 5.43 xc3x85, while the cubic crystal system of SiC has 4.36 xc3x85, which is considerably different. However, by properly selecting the carbonizing state of the Si surface, it is possible to allow a single-crystal SiC to grow on the Si. The cubic single crystal SiC is formed so that the lattice unconformity does not develop so much, since SiC and GaN (lattice constant: approximately 4.5 xc3x85) have lattice constants comparatively close to each other. Thus, it is possible to obtain a semiconductor light emitting device that is less susceptible to crystalline defects.
In particular, the above-mentioned silicon carbide layer is successively formed after the carbonizing process of the silicon substrate, with the result that the SiC layer is formed in the cubic crystal system, and the gallium nitride type compound semiconductor layer is also allowed to have a cubic crystal; thus, it is possible to easily laminate a semiconductor layer that is conformed to the Si substrate in the crystalline property. This method is based upon the idea that instead of the conventional idea that a gallium nitride type compound semiconductor needs to grow in the hexagonal crystal system, even a gallium nitride type compound semiconductor having the cubic crystal system is allowed to provide a high-efficiency light-emission if there is no crystalline defect.
Furthermore, the buffer layer made from a compound containing Ga and/or Al and N is interpolated between the silicon carbide layer and the semiconductor lamination section so that it is possible to absorb the lattice unconformity between the silicon carbide layer and the gallium nitride type compound semiconductor layer.
Additionally, in addition to AlzGa1xe2x88x92zN (0xe2x89xa6zxe2x89xa61), the compound containing Ga and/or Al and N may include another element to be added thereto as a substituent or a dopant.
In the case when the semiconductor lamination section has a structure in which it is sandwiched between an active layer and the n-type layer and p-type layer made of a material having greater band gap energy than the active layer, the light emitting efficiency is enhanced, and a high luminance light emitting diode or a high-output semiconductor laser is obtained.
A semiconductor laser is provided with a silicon substrate, a silicon carbide layer formed on the silicon substrate, and a semiconductor lamination section formed on the silicon carbide layer, and the semiconductor lamination section is made of a compound semiconductor of a Group III element and nitrogen, with the active layer being sandwiched between the n-type layer and the p-type layer having a band-gap energy greater than the active layer as well as having a refractive index smaller than the active layer.
A manufacturing method of a semiconductor laser in accordance with an embodiment of the invention is characterized by the steps of: (a) forming a semiconductor lamination section by laminating a compound semiconductor forming a light emitting layer forming portion on a first substrate having no cleavage, (b) applying a plasma generated from an inert gas on the surface of the semiconductor lamination section so as to expose the dangling bond to the surface, (c) affixing a second substrate having cleavage on the surface of the semiconductor lamination section to which the dangling bond is exposed, with the cleavage face of the second semiconductor substrate being coincident with the cleavage face of the semiconductor lamination section, (d) removing the first substrate and (e) allowing the second substrate to have cleavages to form chips.
Moreover, another method may be adopted in which the first substrate having no cleavage is removed without affixing the second substrate to the surface of the laminated semiconductor lamination section, and a plasma generated from an inert gas is applied to the exposed surface so that the dangling bond is exposed, and the second substrate is affixed to the resulting surface.
In the case when these methods are used, since the dangling bond is exposed to the surface of the semiconductor lamination section, the bonding process is made only by applying a low pressure onto the substrate without the need of any temperature rise, thereby making the semiconductor lamination section free from stress. Therefore, it is possible to obtain a semiconductor lamination section having superior crystalline properties, and consequently to obtain a semiconductor light emitting device with high efficiency. Moreover, since the bonding is made with the cleavage faces being coincident with each other, it is possible to obtain cleavage with ease.
It is preferable that further comprising the steps of: exhibiting a cleavage face by cleaving one portion of the semiconductor lamination section from which the first substrate has been removed, exhibiting a cleavage face by cleaving one portion of the second substrate to be bonded, and aligning the cleavage face of the semiconductor lamination section and the cleavage face of the second substrate so that the cleavage faces of the semiconductor lamination section and the second substrate are made coincident with each other; thus, it is possible to accurately match the two cleavage faces with each other.
The semiconductor lamination section, which has the hexagonal crystal system, is allowed to have its (11-20) face as the cleavage face, and the second substrate, which has the cubic crystal system, is allowed to have its (011) face as the cleavage face; and the two cleavage faces are made coincident with each other and bonded to each other so that the cleavage face of the semiconductor lamination section is matched with the cleavage face of the second substrate that has superior cleavage.
A semiconductor laser is provided with a laser chip that is bonded onto a sub-mount having a greater thermal conductivity, is characterized in that the laser chip is constituted by a conductive substrate and a Group III nitride compound semiconductor formed on the conductive substrate, and is provided with at least an active layer, a semiconductor lamination section having a first conductivity type clad layer and a second conductivity type clad layer sandwiching the active layer, a first electrode placed on the upper surface side of the semiconductor lamination section, a second electrode placed on the rear face of the conductive substrate, wherein the laser chip is bonded so that the first electrode comes into contact with the sub-mount.
In this structure, since the structure is of a vertical type that allows electrodes to be taken out from both of the upper and lower surfaces of the chip, it is not necessary to place one of the electrodes in a narrow place inside a concave section formed by etching. Therefore, it is possible to avoid an unwanted contact of a bonding agent to a side-face portion exposed by the etching or an unwanted contact between the electrodes. Moreover, since the upper electrode (first electrode) side close to the active layer that easily generates heat is bonded to the sub-mount, it is possible to efficiently radiate heat.
It is preferable to form the conductive substrate as one substrate selected from the group consisting of a GaAs substrate, an Si substrate having a SiC layer formed on its surface and a Ge substrate; thus, a Group III nitride compound semiconductor layer is laminated on the conductive substrate so that a chip of the vertical type that allows the electrodes to be taken out from the upper and lower surfaces is provided.
A semiconductor laser is provided with a laser chip that is bonded onto a sub-mount having a greater thermal conductivity, is characterized in that the laser chip is constituted by a substrate formed by placing a conductive SiC layer on the surface of Si and a Group III nitride compound semiconductor formed on the conductive substrate, and is provided with at least an active layer, a semiconductor lamination section having a first conductivity type clad layer and a second conductivity type clad layer sandwiching the active layer, a first electrode placed on the upper surface side of the semiconductor lamination section, a second electrode placed on the rear face of the conductive substrate, wherein the laser chip is bonded so that the second electrode comes into contact with the sub-mount.
With this structure, the laser chip has laminated layers in which the Group III nitride compound semiconductor layer is laminated on the silicon substrate having Si having a great thermal conductivity on its surface; therefore, it is possible to greatly improve the thermal conduction to the laser chip on the substrate side, and even if the substrate side is bonded in a manner so as to contact the sub-mount, heat generated in the active layer can be released sufficiently. As a result, the thickness of the substrate makes the distant from the surface of the sub-mount to the active layer greater, thereby virtually eliminating the possibility that the bonding agent on the sub-mount is raised to the active layer to cause unwanted short-circuiting.
The sub-mount having a great thermal conductivity is preferably formed by a material in which an insulation film made of AlN or SiC is formed on the surface of an Si substrate; thus, it is possible to efficiently radiate heat through the AlN or SiC having a high thermal conductivity formed on the surface.
The sub-mount having a high thermal conductivity is made from at least one material selected from the group consisting of AlN, SiC, diamond, c-BN and BeO, and has a metal rod that is embedded therein so as to provide conduction from the surface to the rear face of the sub-mount, with one of the electrodes of the laser chip being allowed to conduct to the rear face side of the sub-mount through the metal rod. Thus, it is possible to easily allow one of the electrodes to conduct to the rear face side of the sub-mount, while using the insulation substrate having a high thermal conductivity.
In a semiconductor laser a laser chip is die-bonded onto a sub-mount which is made of an insulation material or is partially made of an insulation material, and the sub-mount is placed on a heat sink section that is being provided with a step with the sub-mount being placed on the lower face on the step and wire bonding being provided between the upper face on the step and the sub-mount.
Here, the heat sink section refers to a base, formed by a metal, etc. that easily radiates heat from the sub-mount, on which the sub-mount of the semiconductor laser is installed.
With this arrangement, although one of the electrodes is not directly connected to the heat sink section electrically through the sub-mount, wire bonding is provided on the upper face of the heat sink section so that it stands virtually as high as the surface of the sub-mount. Therefore, it is not necessary to insert a wire-bonding capillary into a narrow space in the heat sink section, and the wire bonding can be carried out even in the narrow space.
When the sub-mount is made from AlN, SiC, or Si having a surface on which AlN or SiC is formed on the side without the semiconductor laser chip being die-bonded, it is possible to provide better thermal conduction, and consequently to radiate heat generated in the small semiconductor chip efficiently.
In the case when the semiconductor laser chip is made from a Group III nitride compound semiconductor, it tends to easily generate heat, and an insulation substrate having a great thermal conductivity is used as the sub-mount; therefore, the easiness of electrode connection is very effective.
A semiconductor laser includes a laser chip that is provided with a semiconductor lamination section that is made of a Group III nitride compound semiconductor placed on a substrate, and includes at least an active layer and a first conductivity type clad layer and a second conductivity type clad layer sandwiching the active layer, and at least one end face of the end faces constituting an optical resonator of the semiconductor laser chip is formed into a flat face. Moreover, an insulation film, provided as a single-layer film or a multi-layered film including a plurality of films having different refractive indexes, is formed on the surface of the flat face.
Here, the expression that xe2x80x9cthe end face is formed into a flat facexe2x80x9d refers to a state in which irregularities in terms of atoms are not formed on a surface subjected to dry etching, and, for example, such a face includes an end face formed through cleavage and a chemically polished face after having been subjected to dry etching.
With this structure, since the insulation film is formed on the surface of the flat face, it is possible to eliminate irregular reflection caused by the interface to the insulation film, and reflected light is positively returned to the inside of the optical resonator, thereby making it possible to improve the differential quantum efficiency.
The end face serving as the light-releasing face of the optical resonator is controlled with a low reflection coefficient, while the opposite face is controlled with a high reflection coefficient so that most of light, generated only on one of the faces utilized is released; thus, the generated light is utilized very efficiently.
The above-mentioned insulation film with a high reflection coefficient is formed by a multi-layered film, and even number of layers are alternately laminated, each layer having a thickness of xcex/4n (xcex: light emission wavelength, n: refractive index of each insulation film), so that it is possible to increase the reflection coefficient. Moreover, with respect to a single layer film or a multi-layered film, odd number of layers are laminated, each layer having a thickness of xcex/4n (xcex: light emission wavelength, n: refractive index of each insulation film), or a single layer film or a multi-layered film is formed, each layer having a thickness of xcex/2n, so that it is possible to reduce the reflection coefficient.
The substrate may be made from any one of Si, Ge, SiC and GaN, on the surface of which GaAs or SiC is formed, and the end face is formed into a flat face through cleavage; thus, it is possible to obtain a light reflection face like a mirror surface.
Here, in the case when the substrate and the Group III nitride compound semiconductor lamination section is made of the cubic crystal system, cleavage is provided more effectively, and a flatter end face is obtained.
A semiconductor laser in accordance with an embodiment of the present invention comprises, a substrate, and a semiconductor lamination section on the substrate, the semiconductor lamination section being made from a Group III nitride compound semiconductor and including at least an active layer and a first conductivity type clad layer and a second conductivity type clad layer sandwiching the active layer a current constriction layer being made from an insulation material, having a stripe-shaped opening section, and being provided inside the semiconductor lamination section.
With this structure, since the current constriction layer is placed close to the active layer, it is possible to inject a current into the light emitting region effectively, and consequently to simultaneously achieve a reduction in the threshold value and an increase in the quantum efficiency; therefore, it is possible to achieve a high output and high reliability.
The Group III nitride compound semiconductor layer is formed through the lateral growth on the current constriction layer via the stripe-shaped opening section of the current constriction layer so that the current constriction layer made from an insulation material is formed inside the semiconductor lamination section.
In this structure, the second conductivity type clad layer is formed on the upper layer side of the active layer and the current constriction layer is formed in the second conductivity type clad layer or thereon through an etching stop layer made from AlsGa1xe2x88x92sN (0 less than sxe2x89xa60.1) in which GaN or Al composition is small; therefore, Al contained in the clad layers, which is susceptible to corrosion from etching liquid at the time of etching, is not exposed so that the Group III nitride composition semiconductor is allowed to preferably grow thereon without being damaged in its re-growth interface.
In the case when the current constriction layer is made from an oxide of Si or Al and/or a nitride, etching is easily carried out without giving influences on the semiconductor layer, and the current constriction layer having a stripe-shaped opening section is readily formed therein.
Light guide layers may be formed between the first and second conductivity type clad layers and the active layer respectively so as to form a waveguide path.
A manufacturing method of a semiconductor laser has the steps of (a) depositing a buffer layer on a substrate, (b) laminating a light emitting layer forming portion, made from a Group III nitride compound semiconductor formed on the buffer layer, which includes a first conductivity type clad layer, an active layer and a second conductivity type clad layer, (c) forming an insulation film on the light emitting layer forming portion, (d) forming a current constriction layer made from an insulation material having a stripe-shaped opening section by etching the insulation film in a stripe manner and (e) allowing a second conductivity type Group III nitride compound semiconductor to grow laterally on the current constriction layer with the semiconductor layer exposed to the stripe-shaped opening section of the current constriction layer serving as a seed.
Prior to forming the insulation film, the etching stop layer made of a Group III nitride compound semiconductor is allowed to grow, and the insulation film is etched by an acidic solution so that the stripe-shaped opening section is formed without giving influences on the semiconductor layer.
A semiconductor light emitting device is provided with an active layer, made from a Group III nitride compound semiconductor, for emitting light upon injection of a current, and n-type and p-type clad layers, made from a Group III nitride compound semiconductor having band gap energy greater than the active layer, which sandwich the active layer from the respective sides, is characterized in that the active layer is made of a compound semiconductor layer containing Ga, P and N.
The active layer may be formed by a material that is, for example, represented by GaPuN1xe2x88x92u (0 less than u less than 0.5). Moreover, in the case when the active layer has a single quantum well structure or a multiple quantum well structure, it is allowed to emit light with high light-emission efficiency, thereby making it possible to provide a semiconductor laser with a high output.
When the substrate is composed of any one of Si on the surface of which GaAs or SiC is formed, Ge, SiC and:GaN, it is possible to provide chips through cleavage, thereby providing an effective structure in forming a semiconductor laser.
In this structure, a mixed crystal of Tl is obtained with superior crystalline property, and even in the case of light having a long wavelength with a low threshold value such as green light, it can be emitted sufficiently by using a direct transition-type semiconductor; thus, it becomes possible to provide a green light semiconductor laser.
The above-mentioned active layer may be formed by a material represented by a general formula, TlvGa1xe2x88x92vN (0 less than v less than 1). Moreover, in the case when the active layer has a quantum well structure, with the well layer of the quantum well structure being formed by a material represented by the general formula, TlvGa1xe2x88x92vN (0 less than v less than 1), it is allowed to emit light with high light-emission efficiency, thereby making it possible to provide a semiconductor laser with a high output.
A manufacturing method of a semiconductor light emitting device according to an embodiment of the present invention, which has the steps of forming a buffer layer on a substrate by using an MOCVD method, growing a semiconductor lamination section made from a Group III nitride compound semiconductor, containing an n-type layer, an active layer and a p-type electrode so as to be electrically connected with the n-type layer and the p-type layer respectively, wherein at the time of the growth of the active layer, a trivalent thallium compound is introduced as a reaction gas for Tl element sot that the active layer is allowed to grow by a compound semiconductor.